A heavy-duty power shear, such as described in our copending and jointly filed application Ser. No. 72,627 has a frame formed by a pair of upright spaced-apart plates between which is provided a pair of blades. One of the blades is fixed on the plates and the other blade is reciprocal in the plane of the plates in the space between them adjacent the fixed blade. One or both of the plates is formed at the blades with a window so that a workpiece to be sheared, punched, stamped, or otherwise acted on by the machine can be inserted through the window and laid on the fixed blade. Displacement of the movable blade past the fixed blade will carry out the desired metalworking operation.
In order to hold the workpiece firmly against the fixed blade during such operation the shear is provided with a holddown, normally in the form of a flat holddown plate slidably mounted on one of the side plates of the machine frame. This plate can move across the window through which the workpiece is inserted and has an edge that can bear normally downwardly on the workpiece. Thus the plate is slid into engagement with the workpiece and is normally retained against movement, frequently by a standard clamping spindle or the like. Rails provided on the one frame plate guide edges of the holddown plate.
It is necessary to periodically change the movable and fixed blades of such a shear. For such an operation it is normally necessary to remove the holddown plate, so as fully to expose the window in the frame plate through which access may be had to the blades. This is normally accomplished by unbolting one of the guide rails and disconnecting whatever mechanism is used to displace and/or lock the holddown plate on the frame plate. Such an operation not only complicates changing the blades of the machine, but also creates the stronger possibility that the machine will be subsequently improperly reassembled.